21250021 has 16 divisors (see below), whose sum is σ = 23554048. Its totient is φ = 19051200.

The previous prime is 21250007. The next prime is 21250039. The reversal of 21250021 is 12005212.

It is a cyclic number.

It is not a de Polignac number, because 21250021 - 2¹⁷ = 21118949 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (13).

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21249983 and 21250010.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21250001) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 100606 + ... + 100816.

It is an arithmetic number, because the mean of its divisors is an integer number (1472128).

Almost surely, 2^21250021 is an apocalyptic number.

It is an amenable number.

21250021 is a deficient number, since it is larger than the sum of its proper divisors (2304027).

21250021 is a wasteful number, since it uses less digits than its factorization.

21250021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 412.

The product of its (nonzero) digits is 40, while the sum is 13.

The square root of 21250021 is about 4609.7745064157. The cubic root of 21250021 is about 276.9830040791.

Adding to 21250021 its reverse (12005212), we get a palindrome (33255233).

It can be divided in two parts, 212500 and 21, that added together give a square (212521 = 461²).

The spelling of 21250021 in words is "twenty-one million, two hundred fifty thousand, twenty-one".